Study On Spatio-Temporal Characteristics Of Hydro-Chemistry And Water Transformation In The Steppe Basin Of Inner Mongolia

The grassland watershed of the Inner Mongolia Plateau is an important ecological barrier in my country's interior.The evolution of water resources is of great significance to the regional socio-economic development and ecological environment protection.In this study,the Balaguer River Basin was selected as the object.A total of 342 water samples of precipitation,river water,and shallow groundwater were collected during the wet and dry seasons from 2019 to 2020,and their physical and chemical indicators,?D and?¹⁸O were determined,using mathematical statistics and inverse distance.Weight method,Piper three-line diagram,correlation analysis,Gibbs diagram,ion ratio method,principal component analysis(PCA)and chlor-alkali index analysis of water chemistry,stable isotope composition relationships,temporal and spatial changes,water chemistry types and their evolution in different water bodies And driving factors;evaluate groundwater quality through single-factor evaluation and Nemerow index;combine precipitation line,evaporation line,deuterium surplus(d-excess),isotope mixing ratio formula and Hysplit model to reveal the conversion relationship between different water bodies and the source of water vapor.(1)The groundwater in the study area presents a weakly alkaline environment and belongs to freshwater.The?D,?¹⁸O and ion concentrations of atmospheric precipitation,river water,and shallow groundwater present the characteristics of wet periods and dry periods.The spatial distribution of groundwater ion components shows a characteristic of high in the west and low in the east,showing a trend of enrichment from upstream to downstream.There are various types of groundwater water chemistry,with HCO₃^–-Ca²⁺·Na⁺type dominant,HCO₃^–-Ca²⁺type,HCO₃^–-Ca²⁺·Mg²⁺type,HCO₃^–Na⁺type and HCO₃^–-Ca²⁺·Na⁺·Mg²⁺type.The groundwater quality is generally good.NO₃^-is polluted in some areas.The Cl^–in the river water during the high water season is greatly affected by human activities.the upstream water quality is better than the downstream,and the water quality near the river is poor.(2)The main environmental driving factors of hydrogen and oxygen isotopes in different water bodies in the basin are temperature,altitude and groundwater depth.Groundwater?D,?¹⁸O,and river water?D all have a significant negative correlation with altitude.When the shallow groundwater depth is less than 10 m,?D and?¹⁸O change greatly,and when it is greater than 10 m,they tend to be stable.Carbonate rock weathering,water karstification and human activities are the main driving factors for the evolution of the hydrochemical characteristics of groundwater and river water in the study area.The control type of groundwater and river water is rock weathering type.During the high water season,the river has a tendency to change to the evaporative concentration type.Alternative cation adsorption affects the chemical composition of groundwater in the study area.The main mechanism,and with the continuous increase of TDS,the alternating effect gradually strengthens.Carbonate dissolution predominates in groundwater.Different geographical locations are the main control factors of water ions in the high water period.Ca²⁺,Mg²⁺and HCO₃^–,Cl^–and Na⁺in atmospheric precipitation have the same land and marine sources.(3)The water vapor transport trajectory in the study area is mainly long-distance,mainly from the three directions of northwest,northeast and southeast.Mainly affected by the Siberian high pressure,Pacific Subtropical High and the East Asian monsoon.The source of river water replenishment is different in different regions of the Balagar River Basin,and the replenishment and drainage relationship with groundwater is more complicated.There is secondary evaporation during precipitation.The distribution of the deuterium surplus value during the wet and dry periods,which is decreasing from south to north.The left branch in the upper reaches of the wet season is the replenishment of groundwater and precipitation to the surface water.The replenishment rate of precipitation to the upstream river water exceeds50%.In other areas,precipitation and surface water jointly replenish groundwater.The recharge and discharge relationship between surface water and groundwater is different in different river sections.